First things first, the most important thing to do is to plan well. Forward planning is vital to any night sky shot, along with a steady tripod and a warm coat. There are quite a few websites and twitter feeds that can help you with your planning. Even though it only takes about an hour and a half for the ISS to complete an orbit of the planet, you could be waiting quite some time under the night skies before the station appears above. The station only appears for a short time (about 1-2 weeks) and then re-appears again many weeks later. This is due to the orbit of the station above earth.